Method of separating pu from metathesized bipo4 carrier



@ni ed. States IVIETHOD F SEPARATING Pu FROM .METATHE SIZED BiPO CARRIERWilliam -J. Knox, New Haven, Conn., and Stanley G.

Thompson, Richmond, Califl, assignors to the United States of America asrepresented by the United States This invention relates to a process forthe separation of actinide rare earth elements from contaminatingelements and more specifically is concerned with a process forseparating such actinide rare earth elements as plutonium and neptuniumfrom a bismuth hydroxide carrier precipitate.

Plutonium and neptunium are usually formed by the neutron-irradiation ofuranium. -Neutron-irradiation of a uranium mass to produce suchtransuranic elements as plutonium and neptunium is ordinarily stoppedwhen the transuranic elements are present in the mass in very smallconcentration. One of the primary reasons for this is the concurrentproduction of radioactive fission products in the mass in suchconcentration that the radioactivity produced thereby in the massrapidly rises to such large levels that the mass becomes very hazardousto human beings. The separation of transuranic elements from aneutron-irradiated uranium mass requires special techniques because ofthis radioactivity and because of the extremely small concentration ofthese elements in relation to the mass.

One method of separating transuranic elements from a neutron-irradiatedmass which has been found to be most successful is by alternateoxidation and reduction steps with intervening carrier precipitationswhereby the plutonium and fission products are carried from the processsolutions with a carrier precipitate. One such process in which bismuthphosphate is employed as the carrier is set forth in copendingapplication S.N. 478,570, filed in the US. Patent. Oflice March 9, 1943,and entitled Phosphate Method for the Separation of RadioactiveElements; it was patented on July 16, 1957, as US. Patent No. 2,799,553.By means of this process a final bismuth phosphate carrier precipitatecontaining plutonium substantially freed of fission products and theuranium may be obtained. The bismuth phosphate carrier containingplutonium may then be converted into a more easily soluble carrierprecipitate by a metathesis step to form a bismuth hydroxide carrierprecipitate containing plutonium. A process for the carrying out of thismetathesis is described in copending application S.N. 745,108, filed inthe US. Patent Ofiice April 30, 1947, and entitled Metathesis of BismuthPhosphate Plutonium Carrier Precipitate With an Alkali.

A conventional method of recovering the plutonium from such a bismuthhydroxide carrier precipitate comprises the dissolution of theprecipitate in a strong mineral acid followed by the precipitation ofthe plutonium with a carrier such as lanthanum fluoride under suchconditions that the bismuth ions do not precipitates While this methodof recoveryis effective, it does require fairly large quantities of acidto efiect the dissolution and requires the further separation of theplutonium from the lanthanum fluoride carrier before the plutonium canbe obtained in a pure state.

It is an object of the present method to provide a simple and directprocess for the recovery of actinide rare earth elements from a bismuthhydroxide carrier precipitate com taining said elements.

Additional objects of the present invention will be apparent from thefollowing detailed description thereof.

We have discovered that an actinide rare earth such as plutonium orneptunium may be recovered from 2. bismuth hydroxide carrier precipitatecontaining said element by treating the bismuth'hydroxide carrierprecipitate with a dilute solution of nitric acid. This treatment of thebismuth hydroxide carrier precipitate with dilute f nitric acidwillresult in the actinide rare eath dissolving in the dilute'acid, whereasthe bismuth hydroxide -precipitate does -not dissolve therein." Althoughwe do not wish to be bound by any theory advanced, it is believed thatthe bismuth hydroxide is converted to the bismuth oxynitrate salt andthat it is this salt which is insoluble in the dilute nitric acid.

The concentration of the acid used as the wash is important, since aconcentrated nitric acid will dissolve not only the actinide rare earthhydroxides, for example plutonium hydroxide, but also the bismuthhydroxide. It is therefore essential that the aqueous solution used todissolve the plutonium be less than about 0.5 N in nitric acid. Apreferable range of acid concentration has been found to be about0.05-05 N with solutions of about 0.1 normality in HNO giving the bestresults. Higher acid concentrations give somewhat increased reactionspeeds, but at the expense of a lowered separation factor,- whereaslower concentrations are in general too slow for plant operations. Theamount of acid used will in general vary with the conditions of use, but10 to 15 ml. of 0.1 M HNO;, per gram of bismuth will in general givesatisfactory solution in a reasonable time.

The temperature of the reaction vessel is not critical and dissolutionat room temperature may be effected in a reasonable time. Variousmethods of contacting the bismuth hydroxide carrier precipitate with theacid solution may be used, and the process of this invention isextremely flexible as to the equipment in which it may be carried out;thus it may becarried outin a centrifuge bowl, a tank reactor, or in anyother suitable apparatus. It is desirable that the reaction be carriedout with agitation. Thus, for large scale operations, a very convenientmethod is to carry out the metathesis of bismuth phosphateplutonium-containing precipitate in a centrifuge bowl and, after washingthe carrier precipitate in the bowl, the nitric acid solution may beadded directly to the centrifuge bowl and slurried in the bowl. Uponcompletion of the dissolution reaction the plutonium-containing solutionmay be separated from the bismuth oxynitrate cake by centrifugation.

Now that the process of this invention has been described it may beillustrated by the following example.

Example A bismuth hydroxide carrier precipitate cake containing 1250 mg.of bismuth hydroxide and 12 mg. of plutonium hydroxide was slurried with15 ml. of 0.1 N I-INO solution for 30 minutes. The slurry was thensubjected to centrifugation whereby the plutonium-containing liquidmedium was separated from the bismuthcontaining solid. Two more washeseach with 15 ml. of

Patented May 31, 1 960" all novelty inherent in the invention as broadlyas possible in view of the prior art;

What is claimed is:

1. A process of recovering an actinide rare-earth from a bismuthhydroxidecarrier precipitate whichcornprises washing said'preeipitate'with an aqueous solution ODS-0.5 N in HNO whereby thetransuranic polyvalent actinide rare earth is dissolved, and separatingthe aqueous solution from the insoluble bismuth precipitate.

:2. The process ofvclaim, 1 wherein the actinide rare earth is uranium.r I p 3. The process of claim 1 wherein the .acti'nide rare earth isneptunium.

4. The process of, claim 1 wherein the actinide rare earth is plutonium.

'5 The process of recoveringplutoniuin-fi'oni a hismuth hydroxide.carrier precipitate which. comprises washing said precipitate with 10-15ml. 0.1 M HNO,

per gram of bismuth, whereby the plutonium is dissolved in saidsolution, and separating said'solution from the insoluble bismuthprecipitate. 7

part 5,"page" 209 (1936); published by Chatles-Griflin &C'o.,-Ltd.',London. Y

Seaborg-et-211.: TheTransuranium Elemen ts;l part -I,

7 page 64 .(1949), published-as-IV-MB of the National 15 York.

Nuclear Energynseries McGraw-Hill Book Co.-, New

1. A PROCESS OF RECOVERING AN ACTINIDE RARE EARTH FROM A BISMUTHHYDROXIDE CARRIER PRECIPITATE WHICH COMPRISES WASHING AND PRECIPITATEWITH AN AQUEOUS SOLUTION 0.05-0.5 N IN HNO3, WHEREBY THE TRANSURANICPOLYVALENT ACTINIDE RARE EARTH IS DISSOLVED, AND SEPARATING THE AQUEOUSSOLUTION FROM THE INSOLUBLE BISMUTH PRECIPITATE.